1. Field of the Invention
The present invention relates generally to thermal protectors and more specifically to a self heating thermal protector for use in protecting recessed incandescent lighting fixtures.
2. Background of the Invention
Recessed fixtures provide architecturally desirable illumination in homes, offices and commercial buildings. Offices and commercial buildings are generally designed for hung ceilings to accommodate electrical conduit and heating and ventilating ducts. In the past the space above the ceiling has been either empty or filled with the aforementioned equipment with air spaces between the equipment. Under these conditions the greatest danger has been overlamping, a condition which exists when a lamp of larger wattage than the fixture is rated for is installed in the fixture. When a larger wattage lamp is used, the heat generated in the fixture is not dissipated quickly enough and the fixture temperature increases to a level that is higher than intended by the fixture designer. If the fixture is operated with the larger lamp, the resulting fixture temperature will rise to a point where charring of plastic parts and wire insulation within and about the fixture can occur. Eventually, deterioration of the fixture components may result in a fire. Fires from overheated lighting fixtures have caused extensive property damage.
Currently, because of increased concern with energy conservation, local and federal agencies are sponsoring programs in which homes and commercial buildings are being insulated as they are built. Existing homes and commercial buildings are normally insulated by forcing thermal insulation into the spaces which are to be insulated.
Building codes require that a barrier be constructed around recessed fixtures to prevent thermal insulation from coming into contact with the fixture. For new structures the foregoing requirement is costly but feasible. The installation of barriers around recessed fixtures in existing structures is relatively expensive and difficult to achieve.
Materials used in the construction of recessed fixtures are thermally rated for the application. Such materials are lamps, sockets, wire and insulation to name a few. The overheating problem due to overlamping and of thermal insulation installed in contact with the fixture exists with all type of fixtures but may be particularly serious with respect to recessed incandescent fixtures.
The possibility of relying upon the heat generated by the lamp in its fixture and its rate of dissipation as an indicator of safe operation has been considered. However, because of the variety of fixtures and lamp sizes and the cost involved of adapting a thermal protector to each specific application, a universal solution of using a self heating thermal protector described herein is proposed.
Safe operation of a recessed fixture depends upon the fixture dissipating a predetermined quantity of heat to its surroundings. The required heat flow is obtained by the air in contact with the fixture removing the heat. The air in contact with the fixture will heat up as it absorbs heat and the heated air, being lighter, rises allowing cooler air to flow in. This continual movement of air dependably cools the fixture. If air movement is restricted by thermal insulation, heat build up will occur resulting in a dangerous situation.